High Compression Ratio Problem

[GeofP]

Thanks Paul

 

I did the new calculation and the CR comes out at 11, as you say.

 

A gasket thickness of 1.6mm would give me a CR of 10.6

 

I have read in a few places on the web that the crushed thickness of a standard pinto gasket is 1.6mm. If I could find one of those, that would solve the problem but the one I bought recently on line is only 1.5mm un-crushed.

 

Geof

[Guest lotusPaul]

You can get a cometic multi layer gasket from tge likes of burton power. I have heard that these need ultra flat surfaces to seal properly tho. Give them a call and see what they have, then do a web search and see if you can get it cheaper.

From those hard working memory cells im thinking a standard gasket is around £25 and a top dog thick item can add £100 to that.

They can also advise on cam choice, perhaps you can broker a deal??

[Snapperpaul]

Big discussion on sealing MLS ( multi layer steel) gaskets such as Cometic and Athena, consensus was to use spray blue hylomar between the individual steel sheets and the surface as the very thin Viton surface coating will not seal rough surface

[GeofP]

Thanks, I looked at the Cometic and Athena gaskets but have decided to use a 0.5mm stainless steel shim from Gosnay's Engineering company with a standard head gasket (compressed thickness about 1.3mm). This will result in a CR of about 10.5.

 

For the shim / block interface I will use spray Hylomar or liquid Wellseal.

 

Now back to the original problem of estimating if the camshaft will cause the valves to hit the pistons.

[Guest lotusPaul]

Geof.

 

Option one,I think you will still have to do a dummy build to be 100% accurate.

 

Option two,fit the cam and retard it slightly. This will ensure that the piston is further down bore at peak valve lift.

 

Paul

[GeofP]

So, I have done a trial build using a compressed gasket, playdoh in the combustion chamber and my existing cam. I turned the crank over 4 revolutions to go through 2 valve cycles and achieved some good impressions in the playdoh.

 

Exhaust valve clearance to top of piston is 7.4mm and inlet valve 5.8mm, probably +- 0.5mm. I understand that a suitable minimum clearance is 2.5mm so this looks good.

 

Now I have to estimate the clearances with a higher lift cam.

[GeofP]

Here is the playdoh on top of the piston

 

 

Edited August 9, 2017 by GeofP

[GeofP]

Seem to have this extra post which I can't delete!

Edited August 9, 2017 by GeofP

[Guest lotusPaul]

Geof, what cams were fitted when you done that?

[GeofP]

Paul, the cam is from my original engine in the 1980 Cortina 2.0 litre estate car with Weber 2V carburettor.

 

The Haynes manual says the following:

Inlet cam lift = 6.33mm, valve lift = 10.12mm, opens 24° BTDC, closes 64° ABDC

Exhaust cam lift = 6.33mm, valve lift = 10.14mm, opens 70° BBDC, closes 18° ATDC

[Guest lotusPaul]

Options in my opinion based on the whole posts.

 

Kent FR34

Piper Ohc 134

Newman PH4

 

These are seleccted as short duration but higher lift cams. Will give usable power from low down to redline of 6k. All will work on a standard carb, re calibrated,or better still a set of twin 40s and a rolling road set up.

With a high power ignition system and any of the cams above you would have to have an ignition curve to suit. Less advance is needed. Just a word of warning, not everything is free, with higher lift cams you may experience fingerpad wear at an accelerated rate. Just keep on top of the maint,

 

With the above info ( ie all info in post) a better designed exhaust system can be developed to extract even more.

 

Hope it helps.